Fluid power supply systems



Jan. 30, 1968 F. F. FOLMER FLUID POWER SUPPLY SYSTEMS Jan. 30, 1968 F. F. FOLMER 3,365,884

FLUID POWER SUPPLY SYSTEMS Filed Nov. 8, 1965 5 Sheets-Sheet z INIVENIOR. FANKFFOLMEQ H/S ATTPNE'Y Jan. 30, 1968 F. F. FOLMER 3,365,884

FLUID POWER SUPPLY SYSTEMS v Filed Nov. e, 1965 5 sheets-sheet s www; QI-AL laf/5 A 7' TOE/VE Y United States Patent O 3,365,884 FLUID PGWER SUPPLY SYSTEMS Frank F. Folmer, 26250 Huntington Manor, Roseville, Mich. 48066 Filed Nov. 8, 1965, Ser. N0. 586,745 14 Claims. (Cl. 60-52) ABSTRACT OF THE DISCLOSURE Improvements in fluid power supply systems are disclosed for supplying hydraulic power to double acting hydraulic work devices having differentials in piston areas between the forward and return sides of the pistons thereof comprising a pneumatic cylinder and double acting pneumatic piston operative therein, the piston rods on opposite sides of which form axially aligned forward and return hydraulic rams which operate in forward and return hydraulic ram chambers, respectively. The area of the forward hydraulic ram exceeds that of the return hydraulic ram and this differential in ram areas expressed as a ratio of the return ram area to that of the forward ram area exceeds the differential in piston areas of any of said work devices expressed as a ratio of the return sides of the work device pistons to the forward sides thereof. A reservoir of hydraulic liquid is provided to transfer a make-up quantity of hydraulic liquid to the return ram chamber during the forward stroke of the piston and to receive an excess quantity of hydraulic liquid from said return ram chamber during the return stroke of the piston which make-up and excess quantities each equals an amount by which the cubic capacity of the return ram chamber exceeds the demand for hydraulic pressure liquid on the return sides of the work devices during said forward and return strokes, respectively. The reservoir is also provided to transfer makeup quantities of hydraulic liquid to the forward ram chamber during the return stroke of the piston to replenish hydraulic losses, if any, which may occur in the forward stroke system.

This invention relates to improvements in fluid power supply systems. Its advantages will become apparent during the course of the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a View, partly in section and partly in elevation, of a fluid power supply unit embodying my invention;

FIGURE 2 is an end elevational view of said unit;

FIGURE 3 is a schematic view illustrating an application for said unit in which it supplies hydraulic fluid power to a plurality of hydraulic working cylinders;

FIGURE 4 is a fragmentary elevational View of an opposite end of said unit; and

FIGURE 5 is a sectional view of the structure of FIG- URE 1 along the line 5-5 thereof;

Referring to the drawings in greater detail, 1G' designates a conventional solenoid-operated multi-way valve, in this instance a 4-way valve which is manifolded via a subplate 12 to a pneumatic cylinder 13 in which 0perates a piston 15 having dual piston rods 16 and 18, the

3,365,884 Patented Jan. 30, 1968 which in turn are held under compression by tie rods 25. The end caps 22, 23, carry air seals in the form of O-rings 77 which are under compression by the sleeve 20. The manifold subplate 12 is bolted, as shown, to the end caps 22, 23. The piston rods 16 and 18 are formed integrally with a shoulder 26 between them, and a section 27 adjacent to the shoulder which is threaded as indicated. A centrally apertured disc 29, which is circumferentially fitted with an air seal in the form of an O-ring 30y about its periphery, is slipped over the rod 18 and abutted against the shoulder 26. A nut 32 threadably engages the threaded section 27 and holds the disc 29 in compression against the shoulder 26 to form the piston 15. Apcrtures 21 and 24, formed by drilling the end caps 22, 23, respectively, in different directions, as shown, communicate opposite sides of the piston 15 with the manifold subplate 12 so that depending upon the shifted position of the spool (not shown) of the 4- way valve 10, the apertures 21, 24, are alternately connected to the pressure air supply port 9. The apertures 21, 24, are also alternately connected, respectively, to the exhaust ports 11, 14, at the time one or the other is connected to the pressure air supply port 9. Such connection between the ports 9, 11 and 14, and the apertures 21 and 24, occurs from the internal piping present in the manifold subplate 12 and in the 4-way valve 10, and from the valving present in the latter, including the shifting spool, none of which piping or valving is shown, since it is entirely conventional.

The hydraulic chambers 17 and 19 are formed by castings 33 and 34 respectively which bolt to the end caps 22 and 23 respectively. The castings 33 and 34 are formed with apertures 35 and 36 respectively in their closed outer ends. The inner ends of the castings 33 and 34 are formed with flanges as shown to bear against respective bushings 3'/ and 38 which are disposed with- 1 in sockets formed in the end caps 22 and 23, respectivefree ends of which function as hydraulic rams. The maniy fold subplate 12 has an inlet port 9 which is connected to a source of pressure air via an air pressure supply line (not shown) and two exhaust ports 11 and 14 which may exhaust to atmosphere or to an air return line, if one is used. The rod 16 is the forward ram and operates within an hydraulic chamber 17, while the rod 18 is the return ram and operates in an hydraulic chamber 19.

The air cylinder 13 is made up from a cylindrical sleeve 2li which is sealed at its ends by end caps 22, 23,

ly. The bushings 37 and 38 carry air-oil seals in the form of O-rings 74 and 78, the seals 74 being under compression from the hydraulic rams 16 and 18, while the seals 78 are under compression from the end caps 22 and 23. The end caps 22 and 23 carry oil seals in the form of O-rings 79 which are under compression from the castings 33 and 34. Each of the castings 33 and 34 is formed with a laterally disposed aperture in its side wall which communicates its interior to its exterior. The laterally disposed aperture 75 for the casting 34 is shown in full lines in FIGURE 2 which also shows how a fitting 42 is threaded in such aperture 75. A similar fitting 4l) is threaded in the laterally disposed aperture 75 in the casting 33. The ttings 40 and 42 in turn are connected with hoses 44 and 45 which communicate with a hydraulic reservoir 46 bolted, as indicated by the bolts shown to the tops of the end caps 22 and 23.

The reservoir 46 is filled with hydraulic fluid, such as hydraulic oil. Sight glasses 47 and 48 are provided at opposite corners of the reservoir for viewing the level of hydraulic oil therein. Within the reservoir 46 and in communication which the hose 44 via a transverse aperture 43 in the reservoir wall is a check valve 58 of conventional design, the check 73 of which is in. the form of a piston as shown and operates to prevent oil from entering the reservoir from any amount of pressure in the hose 44, but which upon suction being developed in said forward ram chamber permits oil to flow through it in the direction of the arrow shown from the reservoir 46 into the forward ram chamber 17 through the hose 44. In this connection a metering bushing 52 is provided at the inner end of the forward ram chamber 17. It has a through-slot 53 formed through its wall at its inner end which communicates with a longitudinal slot 54 formed part-way into the outer wall of the bushing 52 and which slot 54 extends from the inner end of the bushing to the center of the laterally disposed aperture 75 (FIGURE 5) in the side wall of the casting 33, in which aperture 75 the fitting 49 is threadably engaged. The longitudinal slot 54 has to be aligned with the laterally disposed aperture 75 when the metering7 bushing 52 is press fitted into the casting 33. Such alignment would not be necessary if a circumferential groove were formed on the outer wall of the bushing 52 partway thereinto as in the case of the slot 54. Such groove, of course, would be formed at the end of said slot 54 in alignment with the center of the aperture 75 in the casting 33. As will be described hereinafter, the metering bushing 52 serves to replenish any hydraulic oil which leaks out of the forward stroke system by the suction which develops in the forward ram chamber 17 during the last increment of the return stroke of the forward ram 16. This replenishment comes from hydraulic oil in the reservoir 46, which is drawn into the forward ram chamber 17 through the check valve 50, the hose 44, the fitting 40, the aperture 75, the slot 54 and the through slot 53 in the metering bushing 52.

Within the reservoir 46 is another check valve 56, also of conventional design, which is connected in this case to the return ram chamber 19 via a pipe nipple 49, a transverse aperture 43 in the reservoir wall, the hose 45, the fitting 42, and the laterally disposed aperture 75. The check 76 of the check valve 56 prevents oil from entering the reservoir through such check valve from any amount of pressure developed in the hose 45, but permits oil to flow through it in the direction of the arrows shown from the reservoir 46 through the hose 45, the fitting 42 and the laterally disposed aperture 75, into the return ram chamber 19 upon suction being developed in such return ram chamber from retracting movement of the return ram 18 in the power or forward stroke of the piston 15. The reservoir 46 has a vertically disposed hole 58 drilled into its wall, as shown in FIGURE 1, to intersect the transverse aperture 43, which drilled hole 58 is plugged at its top by a pipe plug 59. Another transverse aperture 61 intersects the drilled hole 58 and is plugged at its outer end by the pipe plug 63. A pipe nipple 62 is threadably engaged in the aperture 61 and carries threadably engaged on it a pressure relief valve 64 of conventional design having a slidable piston element 51 normally blocking off fiow through it side arm pipe 57. The valve 64 has a cap 65 which is removable for adjusting the screw 60 which controls the spring tension of a compression spring 67 which in turn controls the pressure with which the piston element 51 is held in its valve closing position to close off ow through the valve 64. The transverse aperture 66 in the reservoir wall which is plugged by the pipe plug 68 is provided to facilitate adjustment of the adjusting screw 60. Flow through the valve 64 takes place upon a predetermined pressure being reached in the hose 45, which pressure is communicated through the drilled hole 58, transverse aperture 61 and against the piston element 51 of the valve 64 to move the same against the spring 67 so that flow occurs through the side arm pipe 57 dumping oil into the reservoir 46. The reservoir 46 has a cover 76 which is bolted to the reservoir body by socket screws 71 and is filled through a fill hole 69 in the cover 70, which ll hole is capped by the pipe plug 72. The cover 70 has a small vent hole (not shown) in it for maintaining the supply of oil in the reservoir at atmospheric pressure. A pair of hangers 126 which are bolted as shown each to one of the end caps 22, 23 are provided for multi-position mounting of the unit.

The fluid power supply unit embodying my invention is used in applications such as illustrated in FIGURE 3 for suppiying hydraulic power to a double acting hydraulic work device such as the plurality of operating hydraulic cylinders shown in FIGURE 3 which are designated 80, Si, 32 and 83. The cylinders Eff-83 have piston rods 84-37 which must be brought to bear upon a work piece, such as indicated at W for example. In this instance the piston rods 84-87 carry welding point holders 114-117 which hold welding electrodes 118-121 for effecting spot welds on the work W. 123 designates back-up members for the Work W. The piston rods 84-8'7 are powered by pistons 90-93 the positions of which, in the respective cylinders 84)-83 are controlled by flow of forward and return hydraulic oil from my fluid power supply unit which is shown in elevation in FIGURE 3.

Cylinders -83 have pressure or forward ports 94-97 which are connected by the lines 10ft-103 to a manifold 98 for the work or forward stroke of the operating cylinders Sti-S3. The manifold 98 is supplied with pressure fluid from the forward ram chamber 17 via a hose 99 which is fitted into the aperture 35 in the outer end of the casting 33. The operating cylinders Sil-83 have return ports 104-167 which are connected to a return manifold 108 by the lines 110-113. The return manifold 10S is connected to the return ram chamber 19 via a hose 109 which is fitted into the aperture 36 in the casting 34.

The area of the pistons -93 may vary from each other in many industrial applications. In the case of each of the hydraulic operating cylinders Sti-83 there is a differential which exists in the area of the piston on its work or forward side as compared to the area on its return side. The area on the return side is always less than the area on the forward side and the differential in area expressed as a ratio of the area on the return side to that on the forward side may vary anywhere from 30 to 55 percent. By this is meant, using the operating cylinders 80-83 as an example, that the area on the return side of the piston 90 within the operating cylinder 30 may be 3() percent, for example, of the area which exists on the work or forward side of the piston 90. The area on the return side of the piston 91 in the operating cylinder 31 may be 40 percent, for example, of the area on the work or forward side of said piston 91. Similarly the area on the return side of the piston 92 of the operating cylinder 82 may be 45 percent of the area on the work or forward side of such piston 92. In like manner the area on the return side of the piston 93 in the operating cylinder 83 may be 55 percent of the area on the work or forward side of such piston 93. I have designed my power supply unit to handle all such varying ratios of differential piston areas which may be encountered in practice without any adjustment being required for such varying ratios which means that my unit is completely self-compensating for even the worst condition that may be expected to be encountered in industrial applications. Only if the air line pressure is set so low that the hydraulic pressure in the return ram chamber during the return work 'stroke is unable to overcome the spring pressure of the spring 67 which seldom occurs must the pressure relief valve 64 be re-set. I have designed my unit so that the area of the return ram 18 is 64 percent of the area of the forward ram 16 which percentage of 64 is safely above the worst condition expected to be met in practice.

My unit cornes in various sizes which are measured in cubic inches of hydraulic iiuid in the forward ram available as pressure uid. As examples, the various capacities may be as little as ten cubic inches and as large as 48 cubic inches of hydraulic fiuid. Naturally, the number of operating hydaulic cylinders that can be handled simultaneously by my fluid power supply unit must be selected so that the total demand for pressure fluid on the work or forward side of the hydraulic operating cylinders is less than the cubic capacity of the forward ram chamber. Within such capacity any diverse work device having a ratio of differential piston area less than 64% may be accommodated. In the case suggested for the operating cylinder 80 wherein the differential piston area is, say 30%, there is less hydraulic fiuid which returns from such cylinder to the return ram chamber 19 to fill the same so that the 34% deficiency is made up from hydraulic iiuid in the reservoir 46 which is drawn into the return ram chamber 19 by suction developed by the retracting movement of the hydraulic ram 18 out of the ram chamber 19 in the forward stroke of the piston 15. `In the case suggested for the operating cylinder 81, the 2.4% deficiency is similarly made up by drawing hydraulic fiuid from the reservoir 46 into the return ram chamber 19. The operating cylinders `82 and 83 in the cases suggested for them would have deficiencies of 19% and 9% respectively, which are likewise made up from flow of hydraulic uid from the reservoir 46 into the return ram chamber 19.

The piston is shown in its fully returned position in the pneumatic cylinder 13 in which such piston is bottomed in such cylinder. The return ram 18 is in its fully returned position bottomed within the return ram chamber 19. The forward ram 16 is likewise in its fully returned position in which case it is retracted the maximum amount from the forward ram chamber 17. 16a indicates the maximum forward position for the forward ram 16 when the piston 15 is bottomed at the opposite or forward end of the cylinder 13. The operating position for the forward ram 16 in its forward stroke will always lie between the maximum retracted position shown for it in full lines in FIGURE 1 and the maximum extended position shown for it in dotted outline and indicated at 16a since in all case-s the piston 15 will never bottom at the forward side of the cylinder 13. This is because the demand from the operating cylinders will not exceed cubic capacity of the forward ram so that there will always be hydraulic pressure maintained in the forward stroke system, i.e. in the lines, etc. leading to the work or forward side of the pistons in the operating cylinders. To insure this maintenance of hydraulic pressure, the forward stroke system must be free of any trapped air to eliminate `sponginess of the oil in such system for releasing which a bleeder valve 124 is provided on the casting 33. For the same purpose for the return stroke system a bleeder valve 125 is provided on the casting 34. In the forward stroke of the piston 15 the air pressure from the source of pressure aid which is admitted to the cylinder 13 from the inlet port 9 through the aperture 24 on the forward side of the piston 15 is multiplied approximately nine to one so that the hydraulic pressure which is developed in the forward ram chamber 17 is approximately nine times that of the air pressure on the forward side of the piston 15. The reason for this is that the area of the forward ram is approximately one-ninth of the area on the forward side of the piston 15. Similarly, in the return stroke of the piston 15, the pressure air, which is admitted into the cylinder 13, on the return side of the piston 15, from the source of pressure air via the inlet port 9 and the aperture 21 is multiplied in respect to the hydraulic pressure which is developed in the return ram chamber 19. This pressure is approximately fifteen times that of the air pressure on the return side of the piston 15, since the area of the return ram, it being smaller than that of the forward ram as previously explained, is approximately one-fifteenth of the area on the return -side of the piston 15.

The operation of my iiuid power supply system is as follows:

In the power stroke lthe solenoid operated four-way valve 1) is energized and its valve spool is shifted to direct pressure air from the inlet port 9 to the aperture 24 so that such air is admitted to the cylinder 13 on the forward side of the piston 15, which starts its forward stroke to the right as shown in FIGURE 1. Air on the return side of the piston 15 is exhausted out of the cylinder 13 through the aperture 21 and out of the manifold sub-.plate 12 through the exhaust port 14 where such air is exhausted to atmosphere or to an air return line, if there is one. From the movement of the hydraulic `ram 16 oil under multiplied pressure as explained, (approximately nine to one) is `directed to the pressure or forward side of the operating hydraulic cylinders 30-3. The pressure air, that is generally expected to be used in practice and supplied to the inlet port 9 may vary from 30 to 150 pounds per square inch of air presure. This multiplication of pressure in the forward ram chamber occurs, as explained, from the differential between the effective area on the forward side of the piston 15 to the effective area on the forward side of the hydraulic ram 16. The hydraulic ram 16 reaches its maximum forward position somewhere between the full line position shown for it in FIGURE 1, and the dotted outline position for it indicated at 16a depending upon the demand of the operating hydraulic cylinders -83 in respect to the cubic capacity of the forward ram chamber which in turn, as explained, depends upon the size of the particular fluid power supply unit. The pressure oil from the forward ram chamber 17 is directed to the work stroke manifold 98 via the hose 99 and from there admitted to the operating hydraulic cylinders 811-835 on the work or forward side of the respective pistons -93 via the hoses 1110-103 and the inlet ports 94-97.

In the same power stroke the return oil on the return sides of pistons 9093 of the operating cylinders 3114113 is forced out of the` return ports 104-107 and directed to the return stroke manifold 10S via the hoses 1111-113. From the return stroke manifold 10S this return oil is drawn into the return ram chamber 19 via the conduit 109. The return of such return oil to the hydraulic ram chamber 19 is aided by the suction developed in the return ram chamber 19 by the retracting movement of the hydraulic ram 18. As previously explained, the return oil on the return side of the pistons 9th-93 of the hydraulic operating cylinders Sti-83 is always less than that amount of oil required to fill the return ram chamber 19 so that make-up oil is 4taken from the oil in the reservoir 46 by the suction developed in the return ram chamber 19. This make-up oil is drawn through the check valve 56, the hose 45, the fitting 42, and through the laterally disposed aperture 75 in the wall of the casting 34 into the return ram chamber 19. This filling of the return ram chamber 19 occurs automatically `from the reservoir by the suction developed by the return ram 18 being retracted out of the return ram chamber 19 during the forward stroke of the cylinder 15. The: amount of fill which occurs from the reservoir, as previously explained, depends how much `greater the 64% differential area I have built into my fluid power supply unit is in excess of the differential area of the operating hydraulic cylinders 811-83. The forward ram 16 is maintained in its forward position so long as the pistons 84-87 of the operating hy- `draulic -cylinders 811-83 must be maintained in contact with the work W in order to carry out the spot weld or other work operation desired.

Upon completion of the forward work stroke of the operatnig cylinders Sil-83, their piston rods 84-87 must be retracted from the work W and returned to their rest or return positions. This is accomplished by the return stroke of my liuid supply unit which is initiated automatically by de-energization of the four-way Valve 10 by which its spool is shifted by spring pressure to direct pressure air to the return side of the piston 15 via the inlet port 9 and the aperture 21. Air on the opposite side of the lpiston 15 is exhausted out of the cylinder 13 via the aperture 24 and the exhaust port 11 where it is exhausted either to atmosphere or -to an air return line, if there is one. The piston 15 starts backward on its return stroke and must return to the exact same position in which it was when it started the power or forward stroke. This is its rest position shown in full lines in FIGURE 1. By insuring return of the piston 15 to its rest position, the same volume of pressure oil in the forward ram chamber 17 can be dispensed to the hydraulic operating cylinders 81l-83 on the next power or forward stroke of the unit. To insure that the piston 15 returns fully to its rest position, dumping of oil into the reservoir 46 occurs during this return stroke, but only after the operating cylinders 80453 have their pistons 90-93 fully returned to their rest or return positions. The relief valve 64 prevents dumping of oil into the reservoir 46 on this return stroke until a predetermined pressure is built up in the hose 45 which pressure is adjustable by removal of cap 65 and setting of the spring pressure by turning of the screw 60 which controls the force with which the piston element 51 closes off the side arm pipe 57. This pressure is adjusted once for most applications of hydraulic operating cylinders and is set so that all of the operating cylinders are fully returned before the piston element 51 moves to permit ow of hydraulic oil through the side arm pipe 57.

The pressure oil from the return ram chamber 19 is directed to the return stroke manifold 168 via the conduit 159 and from there is directed to the return ports 1M- 17 via the hoses 11d-113 into the operating hydraulic cylinders Sit-S3 on the return sides of the pistons Lil-93. The excess oil in the return ram chamber 17 is forced through the hose d5, through the drilled hole 53, through the pipe coupling 52 and, Iby movement of the piston element 51 against the spring `67, through the side-arm 57 of the pressure relief valve 64 by which such excess oil is dumped into the reservoir 46. Return of the pistons 95-93 of the operating cylinders Sti-S3 occurs under multiplied pressure (approximately 15-1), but this pressure is substantially relieved by the time the return ram 1S reaches the end of its stroke in the rest position of the piston 15. Such relief of the pressure in the return ram chamber is down to a pressure less than that set for operation of the pressure relief valve 64, the result of which is to maintain the pistons gti-94 in their return positions so that they will not drift downward. Because the piston 15 bottoms in this return stroke, the pressure in the return ram is reduced to the ypressure of the oil which is trapped in the return stroke system, i.e., in the conduit 109, the return manifold 108, the return lines 11G-113 in the operating cylinders Sil-S3 on the return sides of the pistons 94?-93, in the hose 45, the drilled hole S8, in the pipe coupling 62, and in the valve 64 up to the piston element 51, the latter being seated and closing off the side arm pipe 57. The oil on the forward side of the pistons 90-93 is directed to the work stroke manifold 98 via the forward ports Sid-97 and the conduits 10ft-193, and from such manifold 98 to the forward ram chamber 17 via the conduit 99. The forward oil on the forward side of the pistons @ti-93, which returns to the forward ram chamber 17 is a fixed volume for any given condition of operating cylinders. During the last increment, such as the last 1/15 of an inch of the return stroke of the piston 15, replenishing of oil in the forward stroke system (the conduit 99, the forward stroke manifold 9%, the forward lines 106- 163 and the forward. side of the pistons 9tl-93 in the operating cylinders S50-83) occurs as the forward ram 16 is retracted out of the forward ram chamber 17. This replenishment is as to any oil which leaks out of the forward stroke system from the forward ram 17 up to the forward side only of the pistons gti-93 in the operating cylinders 85-83. Such replenishments occur through the meteringbushing `52 which allows oil to be drawn into the forward ram chamber 1'7 from suction developed by the forward ram 15 in the last increments of this return stroke. Such replenishing is from the supply of oil in the reservoir de which is drawn through the check valve S6, through the hose 44, through the fitting 40, and through the laterally disposed aperture 75 in the wall of the casting 33 into the forward ram chamber 17. The metering bushing 52 prevents overlling of the forward ram chamber which would occur from suction developed in such chamber 17 during the retracting movement of the forward ram .15 in this return stroke, which suction would otherwise occur all during the return stroke draw oil from the reservoir ddthrough the check valve Si?, the hose d4, and fitting itl as described. With the metering bushing in place, just enough withdrawal of the oil from the reser- Voir 46 occurs during the last increment of the return stroke to replenish losses from leakage in the forward stroke system.

My fluid power supply unit replaces hydraulic power units which must be equipped with large electric motors, gear reducers and pumps and which are more expensive and bulkier. My unit may be used to power hydraulic operating cylinders and other hydraulic work devices for welding, piercing and similar operations and may be used for multi-gun spot welding machines and to power portable hydraulic work devices.

It will thus be seen that there has been provided by my invention improvements in iluid power supply systems in which many thoroughly practical advantages have been successfully achieved. Various modifications may be made without departing from the ambit of the invention as dened by the appended claims.

What I claim is:

1. Means in Huid pressure supply systems for supplying hydraulic 'power to double acting hydraulic work devices having differentials in piston areas between the forward and return sides of the pistons thereof comprising:

(a) a pneumatic cylinder and a double acting pneumatic piston operative therein (b) forward and return hydraulic ram chambers and forward and return hydraulic rams, respectively, operative therein (c) said forward and return hydraulic rams having a differential in ram area therebetween (d) a reservoir of hydraulic liquid (e) means interconnecting the pneumatic piston and said forward and return rams so that the air pressure applied to said piston in one direction is multiplied in the forward ram chamber while suction is developed in its return ram chamber to produce a forward work stroke for said work devices and so that air pressure applied to said piston in the opposite direction is multiplied in the return ram chamber while suction is developed in the forward ram chamber to produce a return work stroke for said work devices;

(f) means interconnecting the reservoir and the return ram chamber so that a transfer of hydraulic liquid occurs from the reservoir to the return ram chamber during the forward stroke of the piston; said transfer of hydraulic liquid being of a make-up amount to fill said return ram chamber and equal to that by which the cubic capacity of the return ram chamber exceeds the demand for return of hydraulic liquid from the `return side of the work device during said forward stroke; and

(g) means interconnecting the reservoir and the return ram chamber so that a transfer of hydraulic liquid occurs from the return ram chamber to the reservoir during the return stroke of the piston; said transfer of hydraulic liquid being of an excess amount to empty said return ram chamber and equal to that by which the cubic capacity of the return ram chamber exceeds the demand for hydraulic pressure liquid on the return sides of the work devices during said return stroke.

2. Means as claimed in claim 1 in which said forward and return ram chambers are aligned axially and said forward and return rams are piston rods on opposite sides of the piston.

3. Means as claimed in claim 1 in which the area of the forward hydraulic ram exceeds that of the return hydraulic ram and the cubic capacity of the forward ram chamber exceeds that of the return ram chamber.

d. Means as ciaimed in claim 1 further comprising means interconnecting the reservoir and the forward ram chamber so that a transfer of hydraulic uid occurs from the reservoir to the forward ram chamber during the return stroke of the piston.

5. Means as claimed in claim 4 further comprising a metering bushing in the forward ram chamber by which such transfer of hydraulic liquid from the reservoir to the forward ram chamber occurs during the last increment of said return stroke to replenish hydraulic losses in the forward work stroke system.

6. Means as claimed in claim 1 in which said lastmen tioned interconnecting means between the reservoir and the return ram chamber comprises a pressure relief valve in said reservoir yby which such transfer of hydraulic liquid from the return ram chamber to the reservoir during the return stroke of the ypiston occurs only upon a predetermined pressure being reached in said return ram chamber.

7. Means as claimed in claim 3 in which the cubic capacity of the forward ram chamber exceeds the demand for hydraulic pressure liquid on the forward sides of the work devices in the forward stroke thereof, the cubic capacity of the return ram chamber exceeds the demand for hydraulic pressure liquid on the return sides of the work devices in the return stroke thereof, the differential in ram areas between said forward and return hydraulic rams expressed as a ratio of the area of the return hydraulic ram to that of the .forward hydraulic ram being greater than the differential in piston areas between the forward and the return sides of the pistons of any of said work devices expressed as a ratio of the area on the return side to that on the forward side.

8. Means in uid pressure supply systems for supplying hydraulic power to double acting hydraulic work devices having differentials in piston areas between the forward and return sides thereof comprising:

(a) a pneumatic cylinder and a double acting pue-urnatic piston operative therein (b) forward and return hydraulic ram chambers and forward and return hydraulic rams. respectively, operative therein to `produce forward and return work strokes for said work devices (c) said forward and return chambers being axially aligned and said forward and return rams being piston rods on opposite sides of the piston.

(d) a reservoir of hydraulic liquid;

(e) means including a uni-directional check valve interconnecting the reservoir and the return ram chamber permitting ow of hydraulic liquid from the reservoir through said check valve into said return ram chamber during the forward stroke of the piston; and

(f) means including a uni-directional pressure relief valve interconnecting the reservoir and the return ram chamber permitting ow of hydraulic liquid into the reservoir from the return ram chamber upon a predetermined pressure being reached therein during the return stroke of the piston.

9. Means according to claim 8 further comprising:

(a) means including a unidirectional check valve interconnecting the reservoir and the forward ram chamber permitting flow from the reservoir through said check valve into said forward ram chamber during the return stroke of the piston.

10. Means according to claim 9 further comprising:

(a) a metering bushing in the forward ram chamber 1) by which such fiow from the reservoir through said check valve into said forward ram chamber occurs during the last increments of said return stroke to replenish losses of hydraulic liquid in the forward stroke system.

11. Process in fluid pressure supply systems for supplying hydraulic power to double acting hydraulic work devices comprising:

(a) applying pressure to a rst source of hydraulic liquid via air pressure acting in one direction to multiply such applied pressure from said air pressure for supplying the demand for hydraulic pressure liquid on the forward side of the work devices in their forward work stroke.

(b) simultaneously developing suction in a second source of hydraulic liquid. via air press-ure for supplying the demand for return of hydraulic return liquid from the return sides of the work devices in said work stroke (c) and transferring hydraulic liquid from a third source to the second source by said suction to make up a deficiency by which the amount of returned hydraulic return liquid from said return sides is less than the cubic capacity of the second source.

12. Process according to claim 11 further comprising:

(a) supplying pressure to said second source via air pressure acting in the opposite direction to multiply such applied pressure from said air pressure for supplying the demand for hydraulic pressure liquid on the return sides of the work devices in their return work stroke (b) smultaneously developing s-uction in said rst source via such oppositely acting air pressure for supplying the demand for return of hydraulic return liquid from the forward sides of the work devices in said return work stroke (c) and transferring hydraulic liquid to said third source from said second source by such pressure applied thereto in said return Work stroke to accommodate the excess by which the cubic capacity of the second source exceeds such demand for hydraulic pressure liquid on the return sides of the work devices in their return work stroke.

13. Process according to claim 12 in which such transfer -of hydraulic liquid from the second source to the third source in said return stroke occurs upon a predetermined pressure being reached in said second source near completion of said return stroke.

14. Process according to claim 12 further comprising transferring hydraulic liquid from said third source to said first source by such suction developed in the latter during the last increment only of said return stroke so as to make up losses in hydraulic liquid which may occur between said rst source and the forward sides of the Work devices.

References Cited UNITED STATES PATENTS 2,536,881 l/1951 Lytle 60-52 X 2,573,993 ll/ 1 Sedgwick 60-5 1 2,938,347 5/1960 Sturgis 60-52 EDGAR W. GEORGHEGAN, Primary Examiner. 

